There are different versions of Tableau.
Register an account with Tableau, and watch this videos to get started.
For your assignment, you need to connect the return data with order data by matching order IDs. Tableau has a join function to make this work. To learn more about join, take a look at this Join Your Data page.
Before you publish your visualizations, you can create either a dashboard or a storyboard. The dashboard is to have visualizations on one canvas, while storyboard looks like a photo book that you can flip.
To learn more, watch the videos on dashboards and stories.
Once everything is ready, you can publish to Tableau online. Watch the video on publishing and embedding vizzes.
Remember, you can only publish visualizations you created using public dataset. Do not publish something you created using data that is not publicly available. You can also disable data download so that people can only download your visualizations, but not your raw data.